Process of manufacturing cellulose acetate



Patented Nov. 18 1924.

UNITED STATES 1,516,225 PATENT OFFICE.

I WILLI M B. warn, or nocnnsrna, NEW YORK, ASSIGNOB ro xonsx eonranx, oraoennsrnn, NEW YORK, A CORPORATION or NEW YORK.

PROCESS OF MANUFACTURING CELLULOSE ACETATE.

Application med November 15, 1928. Serial-Io. 875,004.

To all whom. it may concern: Be it known that I, WILLIAM R. WEBB,

a citizen, of the United States of. America, residing at Rochester, inthe county of Mon- 6 roe and State of New York, have invented certainnew and useful Improvements in Processes of Manufacturing CelluloseAcetate, of which the following is a full, clear,

and exact specification. 10 y This invention relates to the manufactureofcellulose'acetate. One object of the invention is to substantiallylessen the cost of such manufacture. Another object is to provide aprocess'in which acetic values,

such'as acetic acid or acetic anhydride, or

both, can be quickly and inexpensively re- -moved from the reactionmixture and recovered in concentrated form. Still another object oftheinvention is to provide a process in which thesurface of the reactionmixture is greatly increased b spraying, in order to facilitate. therapi taking up of vapors of acetic values by means of a gaseous vehicle,such as air. Afurtherobject ofthe invention is to obtain the celluloseacetate from which the bulk of acetic values have been removed, in apowder form that is convenient to manipulate and has a large aggregatesurface, relative to its mass, which facilitates and renders uniform afurther treatment by liquids, such aswashes, reaction .baths, andsolvents. pear.

In the drawing the single figure is a diagrammatic side elevationshowing one form of apparatus in which my process may be convenientlycarried out, the relative sizes of the parts being exaggerated .for thesake of clearness. I Cellulose acetate is produced b the action ofacetylating agents on cellu ose in the presence of catalysts. Thereaction mixture may, for example, comprise cellulose, acetic anhydride,acetic acid and sulfuric acid and as the reaction progresses the masscontains various reaction products including i cellulose acetate. Anexample of this general ty tail in S. Reissue Patent No. 12,637,. Miles,Apr. 23, 1907. Of course, in place of sulfuric acid any other liquid orsolid condensing aglent known in the art may be substituted.

T e acetylating reaction at first forms a chloroform-soluble celluloseacetate. Then cooperate Other objects will hereinafter ap- 'tremelylarge of reaction'mixture is, given in decovery of the acetic valuestakes av hydrolyzing mixture, which includes a relatively small amountof water, is introduced and reaction carried on until the celluloseacetate reaches the acetone-soluble stage. Before the hydrolyzingmixture acts, the excess or unused acetic anhydride is converted intoacetic acid by react' with the proper amount of water. S eient water canbe introduced in the hydrolyz' mixture to kill the acetic anhydride'anin the conversion of the cellulose acetate. At the end of thechloroform-soluble stage there remain considerable amounts 7 of aceticvalues in the mixture, such as'acetic anhydride and acetic acid (and insome cases acetyl chlorid). When the acetonesoluble condition isproduced, the acetic values are practically all in the form of aceticacid. These acetic values are relatively expensive and consequently theamount of them which is used up. in the process has recoverysubstantially in condition for further acetylation, when effectedinexpensively, lowers the total costof the manufacturmg operations andthereby cheapens the cost of the product. g

It has'been previously roposed to wash the reaction mixture with aconsiderable excess of water to free it from the acetic values andprecipitate; the cellulose acetate. Since the values are thus broughtinto dilute solutions, they can be recovered only atan undesirableexpense. 'The evaporation and chemical reactions have proven to beeither too complicated or too costly.

I have found that the recovery of the acetic .values can be carried outat greatly reduced expenseand trouble by spraying the reaction mixtureinto a desiccatlng gaseous vehicle, such as air, which takes 11 vaporsof said values from' the spray an thereby converts'the latter into apowder which is relatively dry.- The taking :up of the vapors and theconversion into powder take place very rapidly, because of the ex ag tosurface of the sprayed particles ative to their total mass.

I have furthermore discovered that the replace more thorou hly andmoremexpensiveliy; ifthegaseous v hiclebe passed not only t rough thezoneswhere, the spraying and dryi topowder take .place, but also tozones w ere the vapor is removed. In the preferred form of 119 ,ing,condensing and reheating zones.

in sequence through the spraying and using the same. gaseous vehicleover and over.

so that the e again high concentrations of.vap,ors of acetic values are1nsured, w1th consequent ease in condensing or absorbing them. Sincecomplete removed of the vapors of acetic values from the gas is notadvisable (because solid acid forms and clogs the condenser at too lowtemperature) the gas would carry away waste and unextracted vapors, ifdischarged into the atmosphere. Recirculation prevents such loss. Thepowder formed in the process is in a very convenient form forstorage andfor further treatment. By reason of its very great surface everyparticle of it is rapidly actedu on in any fluid treatment,

' fi ects are substantially uniform,an important feature when operatingon a manufacturing scale. If reaction liquids act more rapidly on someparts of the material to be treated than they do on others, aheterogeneous mixture of irreglv larly reacted material is apt to occur.

Of course 'many forms of apparatus may be emplo e for carrying out myprocess, the one shown in the drawing. being merely illustrative of onetypical species.

Into a drying and powder-collecting chamber 1 the reaction mlxture isspraye from sprayin chamber 2, the desiccating aseous vehic e, such asheated air, being orced intocontact with the spray so as to uickly takeup vapors of'acetic values from the fine 'atomlzed particles to such anextent that the latter form a relatively ,dry powder which collects inthe bottom of the chamber 1 and may be removed through the door 3. Thevehlcle carryingthe' vapors thenpasses through ipe 4: into an suitablecondenser 5, the con ensed values eing collected in section 6 thereof.The gaseous vehicle, deprived of a large part of its entrapped vapors,then passes through pipe 7 to blower or com ressor 8, and thence throughpipe 9 to t is reheating station 10. From the latter it again passesinto the nozzles or other directing devices of chamber 2;

The units of, this apparatus are well known to those skilled in the artand consequently the details of them need not be described. The sprayingand drying chambers and their accessories may be substantially ofthetype indicated in U. S. Letters Patent No. 1,183,098, Merrell, etal., May 16, 1916, desiccating apparatus, N 0. 1,141,879, Merrell, et9.1., June 1, 1915, desiccatin process, and No. 1,183,393, Merrell, etal., ay 16, 1916, spraying nozzle, these applying the general principlesof No. 666,711, 'Stauf, Jan. 29., 1901, method of desiccating blood. Ofcourse, the parts of the apparatus are made of materials especiallyresistant to the corrosive action of acetic acid and acetic anhydrideand the other active compounds of the reactionmass. The application ofaluminum, copper, bronzes, corrosion-resisting ferrous materials, suchas iron-chromium alloys and the like, can be readil made where needed,as will be understood y anyone skilled in the art. i r

In carrying out my process in this apparatus, by way of illustration,the reaction mixture, such as one of those shown at the difierent stagesof the Miles patent cited above, (or one having a solid condensing agentwhich facilitatesthe powdering) is charged into chamber 2 in the, usualway.

-Here it is blown through a nozzle into" a fine spray ormist and is brouht into intimate contact with a current 0 warm, dry air which acts asthe desiccating vehicle. The

it, the vapor-laden air passes out to a valueremoving zone. This maytakethe form of one of the well known' absorbing towers in which theacetic acid and acetic anhydride are absorbed in suitable liquids; but Iprefer to use a condensing apparatus 5 in which the vapor-laden air israpidly chilled to a temperature at which a large part of the vapors arecondensed. I have found 60 F. to be useful, because it avoids cloggin bythe formation of solidified values, but 1t is susceptible ofconsiderable variation. The liquid acetic acid and other values are thencollected and withdrawn.

The gaseous vehicle then contains no more acetic values thanthosecorresponding to the vapor pressures of such values at the condensintemperature. The vehicle passes throng 1 the compressor or blower 8,which forces it through pipe 9 and reheater .10. The latter is adaptedto bring the temperature of the gas to such a point that when t e warmedgas is blown from chamber 2 into chamber 1 itwill be at the correcttemperature for desiccation of thespray without impairing the latter. Agood working temperature is150 F. Of course, this can be,

varied. considerably according to the particular constitution of thereaction mixture;-

but it preferably should not range much above 180 F, because impairmentof the product maytake place. ith the customary reaction mixtures Iprefer to keep with (ill ' liquids in further weight of celluloseacetate.

erations. contains some residual amounts of acetic acid vapor. But theseare sutliciently below the saturation point, at the temperature producedby the reheating, to avoid interference with the quick and thoroughdrying of the spray.

Vhile the vapors of acetic values may be absorbed by bubbling thevapor-laden vehicle through a suitable liquid and then separating thevalues from such liquid, nevertheless, I find it preferable to use thecondensing method, .an example of which is given above, because itavoids further unnecessary distilling operations, and because it obtainsthe acetic values in a form pure enough for reuse in furtheracetylation. The freedom of the recovered acetic values from impuritiessuch as volatile mineral acids, may be insured by using the expedientsset forth in my application, Serial No. 662,910, filed Sept. 15, 1923,for process ofmanufacturing cellulose acetate.

The finished powder, because of its exceptionally large aggregatesurface relative to its mass, can be very rapidly treated by steps ofmanufacture, such as by wash water or baths or hydrolyzing mixtures, orby solvents, etc. The powder will remain as such even when considerableamounts of acetic acid are left in it, for instance when there isslightly more than 1 part of acetic acid by weight for 1 part ofcellulose acetate. I prefer, however, to conduct the process asdescribedabove, so that the amount of acetic acid left in the powder is onlyabout one-quarter or less of the This small residuum of acetic acid doesno harm in the further operations of the process, especially when thespraying and powdering is done at the end of the chloroform-solublestage, because the small amount of acetic acid cooperates with the mainliydrolyzing acid in converting the material to the acetone-solubleform. I consider the powder to be relax tively dry when the particles ofit do not stick together sutliciently to spoil the advantages of thepowder form recited above.

Having thus described my invention, what I claimas new and desire tosecure by Letters Patent is:

1. In the process of manufacturing cellulose acetate, spraying atlowablc cellulose acc-, late reaction mass containing volatile aceticvalues into a desiccating gaseous vehicle which takes up vapors of saidvalues, and converts the spray into a relatively dry powder. 1

2. In the process of manufacturing cellulose acetate, spraying aflowable cellulose acetate reaction mass containing volatile aceticvalues into a desiccating gaseous vehicle which takes up vapors of saidvalues and converts the spray into a relatively dry powder, separatingsaid vapor-laden gaseous vehicle from said powder, and recovering saidacetic values from said vehicle.

3. In the process of manufacturing cellulose acetate, spraying afiowable cellulose acetate reaction mixture containing volatile aceticvalues into a desiccating gaseous vehicle which takes up vapors of saidvalues and converts the spray into a relatively dry powder, separatingsaid vapor-laden vehicle from said powder and cooling said vehiclesufliciently to condense the acetic values therefrom. r

4. In the process of manufacturing cellulose acetate, repeatedly passinga gaseous ve -v hicle through spraying and drying and value-recoveringzones, a flowable cellulose acetate reaction mass containing volatileacetic values being sprayed into said vehicle at the first named zone,vapors of said values being taken up by the vehicle and the spray beingthereby converted into relatively dry powder which is separated, atleast part of said vapors being removed at said recovery zone.

5. In the process of manufacturing cellulose acetate, repeatedly passinga gaseous vehicle through spraying and drying, condensing, and reheatingzones, a flowable cellulose acetate reaction mass containing volatileacetic values being sprayed into said vehicle at the first named zone,vapors of said values being taken up by the vehicle and the spray beingthereby converted'into a relatively dry powder which is separated, atleast part of said vapors being removed at said condensing zone.

6. In the process of manufacturing cellulose acetate, convcrting into afine spray in a current of heated desiccating air a flowable celluloseacetate reaction mass containing acetic acid, said air taking upvapors'of said acid and converting said spray into relatively drypowder, collecting said powder, and separating the vapor-laden air fromthe powder.

7. In the process of manufacturing cellulose acetate, converting into afine spray in a current of heated desiccating air a flowable celluloseacetate reaction mass containing acetic acid, said air taking up vaporsof said acid and converting said spray into a relatively dry powder,collecting said powder, separating the vapor-laden air from the powder,and recovering said acetic acid therefrom.

8. In the process of manufacturing cellulose acetate, converting into afine spray in a current of heated desiccating air a flowable celluloseacetate reaction mass containin acetic acid, said air taking up vaporsof sai acid and converting said spray into a. relatively dry powder,collecting said powder, separating the vapor-laden air from the powder,and cooling it to condense acetic acid therefrom.

, 9. In the process of manufacturing cellulose acetate, repeatedlypassinga current of .desiccating air throng spraying and drying andvalue-recovering zones, 'a flowable cellulose acetate reaction masscontaining acetic acid being sprayed into said air at the first namedzone, vapor of acetic acid being taken up by the air and the spray beingthereby converted into a relatively dry powder which is separated outfrom the air before the latter reaches said value-recovering zone, atleast part of the acetic acid being re- .moved from the air at saidreco\-'ering'zone.

10. In the process of manufacturing cellulose acetate, repeatedlypassing a current of desiccating air through spraying and drybeingthereby converted .into a relatively dry powder which is separated fromsaid air before the latter reaches said condensing zone, at least pa rtof the acetic acid vapors beingcondensed by coolingjat-said condensingzone, and the air being reheated at said reheating zone.

Signed at Rochester, New York, this 6th dayof November, 1923.

WILLIAM R. WEBB.

